Windoku, also known as the NRC Sudoku variant or HyperDoku,
has all the rules of a “vanilla” Sudoku, with
one addition: The four window panes with the blue background color must also contain digits 1 through 9.
Many solving techniques for normal Sudoku can be used, but you will also need to use the 4 windows panes to check for
singles, pairs, triples, and their interaction with rows, columns and boxes. The way the 4 window panes are positioned
allow you to find 5 additional groups of cells where only digits 1 through 9 can go. These implied rules can prove very
useful when you try to solve this puzzle.

Copy the number string below the puzzle and paste it into the SudoCue program, after you have set the variation to Windoku.